In the so-called reaction injection method, two reaction components which in the initial state are still liquidy in the initial state, like polyetherpolyol and polyisocianate, are conveyed by means of dosing pumps to a mixing head and are united to a reaction mixture. The reaction mixture flows from the mixing head through a sprue into the mold and reacts there in the cavity into a solid material, for example polyurethane.
It is known to inject or foam moldings of this type during their manufacture as reaction mixtures onto metallic or plastic surfaces in order to create a composite part in this manner. However, the adhesive connection mainly in the case of plastic-plastic composite parts leaves much to be desired. Aside from this, this type of manufacture requires expensive tools and separate operations during the manufacture of the two composite parts.
The basic purpose of the invention is to provide a device with which the plastic-plastic composite parts made out of reaction mixtures can be manufactured particularly easily and inexpensively in one operation.
The solution of the invention is based on the thought that composite parts of various plastics can be manufactured by injecting from various sprues at least two different reaction mixtures simultaneously or at different times into the cavity of a mold, by the cavity during the injection time of at least one of the reaction mixtures being separated into two or more mutually sealed regions and by cancelling the separation of the cavity regions following the injection time of the one reaction mixture and while at least partially still liquidy reaction mixtures cover the separation plane.
To achieve this at an optimum, the invention suggests the following characteristics:
The cavity can be loaded with different reaction mixtures through at least two sprues and be separated at least at one separation plane at times into mutually sealed regions connected each with one of the sprues; PA1 in the mold in the region of the separation plane there is arranged PA1 The separating slide member or the separating seal has a blocking surface projecting on both sides over the separation plane toward the two adjacent cavity regions and forming at the projecting parts both in the blocking state and also in the opening state a boundary surface of the cavity in the adjacent cavity regions.
(a) a separating slide member movable relative to the cavity or PA2 (b) a flexible separating seal movable under the action of a pressure medium;
The flexible separating seal is advantageously constructed as a rubber-elastic tube arranged in an elongated open border recess and loadable with a pressure medium (pressurized air or hydraulic fluid), a side of which tube, which side lies opposite the border opening, is fastened in the recess on the mold and can be pressed with its end face, which is on the side of the opening, against a separating edge arranged on the oppositely lying mold part thus separating two cavity regions, and which end face can be lifted off from same opening a gap. The width of the gap and thus the wall thickness of the molding in the transition region can be adjusted by selecting the injection internal pressure. The sealing tube is advantageously, bellows-like, expandable and compressible in the recess.
The separating seal has the advantage, compared with a separating slide member movable transversely with respect to the cavity, that it can be utilized also for rounded forms, thus not only in flat separation planes, since it carries out an all over equal path of movement during a change of the internal pressure, but also in angled regions and regions curved relative to one another. Also the mold does not need any additional movable parts which must be separately guided and tempered as this is the case with a separating slide member.
Whereas if inner slide members are needed in a curved region of a mold, the aforedescribed separating slide members and separating seals with a path of movement extending transversely with respect to the cavity are not suited for the temporary separation of the cavity regions. However, separating slide members which can be moved transversely with respect to the opening direction of the mold can here be used advantageously.
Such a separating slide member has advantageously a sealing edge which can be pressed sealingly against a separating edge of the oppositely lying mold part, which separating edge is aligned in opening direction of the mold. Following the sealing edge, the separating slide member has on the one side a boundary wall for the cavity, which boundary wall is aligned substantially perpendicularly with respect to the direction of movement of the separating slide member and borders an overlapping region between the reaction mixtures in two end positions, while the separating slide member has on the other side a cavity boundary wall forming the inside contour of the molding in the opening position of the separating slide member.
According to a further advantageous development of the invention, two spaced apart cavity regions loadable with different reaction mixtures are provided, which cavity regions on its sides facing one another are separated by spaced apart separating edges from a third cavity region loadable with a further reaction mixture. Either a joint separating slide member defining third cavity region or two separating slide members or separating seals, which are independent from one another, can be pressed against the separating edges.
To achieve decorative surfaces, it is possible to insert into one of the cavity regions a foil or fabric blank, which can be foamed from behind by the reaction mixture. The foil or the fabric blank can thereby be clamped in two parts at the separating edge between two molding regions by the separating slide member or the separating seal, with the edge of the blank being able to project beyond the separating edge into the adjacent cavity region and with the respective reaction mixture foaming there around the edge. Panelling parts, for example for interior panellings of doors of motor vehicles which must be divided into multi-colored or differently soft regions, which in turn, if necessary, can be lined with a foil or a textile surface, are preferably manufactured in this manner.
To adjust an optimum connection between the composite parts, the time-sequence control has proven to be advantageous, with which, in accordance with the different injection, start of increasing viscosity and hardening times of the reaction mixtures staggered in time, the various sprues are loaded with the reaction mixtures and the separating slide member or rather the separating seal is controlled.
The device of the invention can be utilized advantageously for the manufacture of bumpers for motor vehicles out of Hard-Pur in composite action with a spoiler of Soft-Pur, which spoiler is near the ground, with the soft lip being able to yield elastically and therefore be free of destruction by possible obstacles, as for example a curb.
A further possibility for use consists in the manufacture of air-inlet screens, panelling parts and body parts for motor vehicles of hard plastic, which in their edge areas are defined by a soft composite lip. Such a lip guarantees on the one hand a tolerance compensation with respect to the adjoining parts and fulfills on the other hand a gap-filling sealing function.